Long-term objectives: This proposal is in response to the PAR 02-049, Research Objective 19, "Genetics, behavior, and aging". The Mec lp (mitotic entry checkpoint) protein regulates cellular senescence and the cycle damage checkpoint in budding yeast. Meclp is related to the human Atm (Ataxia telangiectasia mutated) tumor suppressor protein, and phenotypes detected in mecl cells are similar to those found in cells lacking Atm. Aberrant telomere regulation in mecl cells has been used to screen for potential regulators of Meclp function. The Yvhlp (yeast VH1) protein phosphatase was detected as a potential negative regulator of Meclp. The long term objective of this proposal is to understand the role of Yvh1p in Meclp signaling, then determine the extent to which the human homologue regulates cancer progression. Specific aims: Yvh l p is a candidate inhibitor of Mec l p signaling. To understand the function of Yvh l p in the damage checkpoint and telomere regulation, we will perform the following specific aims. (1) We will the extent to which Yvh l p overexpression regulates damage repair, telomere position effect, and telomere length. (2) We will then determine the extent to which deletion of Yvhlp affects damage sensitivity and telomere function. (3) We will analyze the extent to which Yvhlp regulates senescence and genome stability in strains lacking Mec lp and Tel lp. Research design and methods: Budding yeast strains have been constructed with a marker gene at the telomere. Mec lp is required for the formation of a heterochromatin "cap" at the telomere that suppresses the expression of this marker gene. We will examine the transcriptional regulation of this marker gene in cells that overexpress Yvh l p or do not express Yvh l p. We will analyze the phosphorylation state of Mec lp substrates when Yvhlp is overexpressed or lost. We will combine mutations to YVH1 with mutations to MEC1 and TEL1 and analyze the onset of senescence and genome instability, including dicentric chromosome formation. Health relatedness: Senescence is the end of the cellular aging process, and the onset of senescence is regulated by telomeres. Meclp and the related Tellp regulate telomere structure and senescence in budding yeast. This proposal will examine a putative regulator of Mec lp signaling, and how it effects telomere structure and senescence. This study is related to health because Atm is the human homologue of Mec lp and Tel lp, and Atm is a key regulator of aging, telomere structure, and cancer.